Mendel and Heredity

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Mendel and Heredity
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Section 1- The Origin of Genetics

• Heredity- The passing of traits from parents to
  offspring.
• Example of traits eye color, eye shape, hair
  texture, height

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Gregor Mendel- Father of Genetics1856-1863

• Where was he from?
• What was his profession?
• What organism did he breed different varieties
  of?
• He was first to do what?

Austria

• Monk

Garden Pea

• 
  Develop rules that accurately predict patterns of
  heredity

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• What branch of biology focuses on heredity?
• Genetics

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Why were pea plants so good for studying heredity?

• 1. Traits of the plant were in 2 distinct forms.
  e.g. flower color was either purple or white
• 2. The male and female parts are enclosed in the
  same flower.

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Why were pea plants so good for studying heredity?

• 3. Garden peas are small and have a fast growth
  rate and reproductive cycle.

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What are the 7 traits that Mendel studied in pea
plants?

• .
• 1. Flower color
• 2. Seed color
• 3. Seed shape
• 4. Pod color

• Pod shape
• 6. Flower position
• 7. Plant height

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Traits expressed as Simple Ratios

• Monohybrid cross (mono one)- a cross that
  involves one pair of contrasting traits
• e.g. Crossing purple flower plant with a white
  flower plant

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3 steps of Mendels experiments

• 1. He made sure that the plants he was going to
  use were true-breeding.
• These original parent plants were known as
  the P generation.
• 2. He cross-pollinated plants that had
  contrasting traits. He called the offspring of
  the cross the F1 generation. He then examined
  each F1 plant and recorded the number of F1
  plants expressing each trait.

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3 steps of Mendels experiments

• 3. He allowed the F1 generation to
  self-pollinate and called the offspring of the F1
  the F2 generation. He then again counted and
  characterized each plant.

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3 steps of Mendels experiments

• A ratio is a comparison of 2 numbers and can be
  written as a fraction or with a colon.
• In F2 generation, 705 purple to 224 white forms a
  ratio of 31.
• (3 purple 1 white)

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EOC Prep Question

• When 2 true-breeding pea plants that show
  contrasting forms of a trait are crossed, all of
  the offspring show
• A. Both forms of the trait
• B. One form of the trait
• C. One-fourth of each trait
• D. A different trait

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Section II Mendels Theory

• Before Mendel, many people believed in the
  blending hypothesis in which offspring were a
  blend of their parents. Mendels results did not
  support the blending hypothesis.

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Mendels Hypothesis

• 1. For each inherited trait, an individual has 2
  copies of the gene- one from each parent.
• 2. There are alternative versions of genes.
  Alleles are different versions of a gene.

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Mendels Hypothesis

• 3. When 2 different alleles occur together, one
  of them may be completely expressed, while the
  other may have no observable effect on the
  organisms appearance.

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Mendels Hypothesis

• Dominant- expressed form of a trait
• Dominant alleles are written as capital letters
• Recessive- trait that was not expressed
• Recessive alleles are written as lower-case
  letters.

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Mendels Hypothesis

• 4. When gametes are formed, the alleles in each
  gene in an individual separate independently of
  one another. Thus, gametes only carry 1 allele
  for each inherited trait. When gametes join
  during fertilization, each gamete contributes 1
  allele.

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Mendel in Modern Times

• Homozygous- 2 alleles for a trait are the same.
• Example PP or pp YY or yy
• Heterozygous- 2 alleles for a trait are
  different.
• Example Pp Yy

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Mendel in Modern Times

• The allele for yellow pea seeds is dominant.
• So, Y yellow and y green
• What color seeds would YY have?
• Homozygous or Heterozygous?
• What color seeds would Yy have?
• Homozygous or Heterozygous?
• What color seeds would yy have?
• Homozygous or Heterozygous?

yellow
yellow
green
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Mendel in Modern Times

• The allele for freckles is dominant.
• So, F freckles and f no freckles.
• Would a child with FF have freckles?
• Homozygous or Heterozygous?
• Would a child with Ff have freckles?
• Homozygous or Heterozygous?
• Would a child with ff have freckles?
• Homozygous or Heterozygous?

yes
yes
no
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EOC Prep Question

• If a pea plant is heterozygous for a particular
  trait, how can the alleles that control the trait
  be characterized?
• A. Two recessive
• B. Two dominant
• C. One dominant, one recessive
• D. Three dominant, one recessive

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Mendel in Modern Times

• Genotype- the set of alleles that an individual
  has
• Phenotype- the physical appearance of a trait
• Genotype Phenotype
• F freckles FF freckles
• f no freckles Ff
  freckles
• ff no freckles

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Mendel in Modern Times

• Genotype
  Phenotype
• P purple flower PP
• p white flower pp
• Pp

purple
white
purple
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Mendel in Modern Times

• Genotype
  Phenotype
• Y yellow seed
• y green seed

yellow
YY
yellow
Yy
green
yy
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The Laws of Heredity

• The Law of Segregation- 2 alleles for a trait
  segregate when gametes are formed.

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The Laws of Heredity

• The Law of Independent Assortment- the alleles of
  different genes separate independently of one
  another during gamete formation.
• Example Gene for height separate differently
  from flower color or seed shape

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The Laws of Heredity

• Mendel found the inheritance of one trait did not
  influence the inheritance of another trait.
• For example plant height did not influence the
  inheritance of another trait such as flower color

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The Laws of Heredity

• To study how different pairs of genes are
  inherited Mendel conducted dihybrid crosses. A
  dihybrid cross is a cross that considers 2 pairs
  of contrasting traits. For example a cross that
  considers both plant height and flower color.

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The Laws of Heredity

• Example
• PPYY x ppyy
• purple white
• flowers flowers
• yellow green
• seeds seeds

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Section III Studying Heredity

• Punnett squares- a diagram that predicts the
  outcome of a genetic cross by considering all
  combinations of gametes in a cross
• Punnett squares allow direct and simple
  predictions. Punnett squares show probability,
  NOT actual results.

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Section III Studying Heredity

• Probability- the likelihood that specific events
  will occur.
• It can be represented as a ratio or a fraction or
  a percentage.
• Practice using the
• examples in your notes

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• Dihybrid Cross
• Predictions for 2 triats
• You can predict 2 traits by making a dihybrid
  cross. Use the FOIL method for setting up the
  dihybrid cross.
• F First
• O outside
• I inside
• L last
• Practice on the two examples.

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Inheritance of Traits

• Geneticists often prepare a pedigree which is a
  family history that shows how a trait is
  inherited. Pedigrees are particularly helpful if
  the trait is a genetic disorder and the family
  members want to know if they are carriers.
• Carriers- individuals who are heterozygous for an
  inherited disorder but do not show symptoms

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Inheritance of Traits

• Albinism Pedigree
• What do the squares represent?
• What do the circles represent?
• What does it mean if the shape is shaded in?

males
females
Affected individual
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• Albinism- the body is unable to produce an enzyme
  necessary for the production of melanin
• Albinism is a genetic disorder transmitted by a
  recessive allele.

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Examine Pedigree I, which traces the dimples
trait through three generations of a family.
Blackened symbols represent people with dimples.
Circles represent females, and squares represent
males.

Although Jane and Joe Smith have dimples, their
daughter, Clarissa, does not. Joes father has
dimples, but his mother, and his sister, grace,
do not. Janes father, Mr. Renaldo, her brother,
Jorge, and her sister, Emily, do not have
dimples, but her mother does.
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Inheritance of Traits

• Sex-linked trait- a trait whose allele is located
  on the X chromosome
• Most sex-linked traits are recessive and are
  usually only seen in males.

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EOC Prep Question

• A cross between two pea plants that produce
  yellow seeds results in 124 offspring
• 93 produce yellow seeds and
• 31 produce green seeds.
• What are the likely genotypes of the plants that
  were crossed?

A. Both Yy
C. Both yy
D. One YY, one Yy
B. Both YY
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Traits Influenced by Several Genes

• Polygenic trait- when several genes influence one
  trait
• The genes for a polygenic trait may be scattered
  along the same chromosome or located on different
  chromosomes. Because of independent assortment
  and crossing-over, many different combinations
  appear in the offspring.
• Example eye color, skin color, height, weight,
  hair color

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Intermediate Traits

• Incomplete dominance- when an individual displays
  an intermediate trait
• Example
• 1. cross red snapdragons with white snapdragons
  and make pink ones
• 2. cross straight haired parent with curly
  haired parent child with wavy hair

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Sample Problem

• RR red snapdragon flower
• RW pink snapdragon flower
• WW white snapdragon flower
• Parent 1 is Pink x Parent 2 is white
• RW x WW
• Make a Punnet Square!!!!!!!
• _____ red ____ white ____ pink

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50
0
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Sample Problem

• BB black hair BW grey hair WW white hair
• Parent 1 black hair BB x WW
• Parent 2 white hair
• Offspring
• ___ black ___ grey ___ white
• Make a Punnet Square!!!!

0
100
0
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Traits Controlled by Genes with Three or More
Alleles

• Multiple Alleles- genes with 3 or more alleles
• Example ABO blood types are determined by 3
  alleles
• 4 different blood types are A, B, AB, and O

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Traits Controlled by Genes with Three or More
Alleles

• IA A IB B i O
• Fill in the following blood types with the given
  genotypes
• IA IA ______ IAi ______
• IB IB ______ IBi ______
• IA IB ______
• ii ______

A
A
B
B
AB
O
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Traits with 2 Forms Displayed at the Same Time

• Codominance- both forms of the trait are
  displayed (2 different dominant alleles are
  shown)
• This is different from incomplete dominance
  because both traits are displayed.
• Example ABO blood types- Type AB blood cells
  carry both A and B types

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Traits influenced by the Environment

• The color of the Arctic Fox is determined by
  temperature.
• What color is the fox in summer? ____________
• What causes the foxs coat to darken? _________
• What color does the fox turn in the winter?____
• What advantage is this to the fox?____________

reddish brown
Enzymes that make pigments
white
camouflage
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Genetic Disorders

• In order for a person to develop and function
  normally, the proteins encoded by his or her
  genes must function precisely. Sometimes genes
  get damaged or are copied incorrectly, resulting
  in faulty proteins. Changes in genetic material
  are called mutations.

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Genetic Disorders

• Sickle-Cell Anemia- disorder that produces a
  defective form of the protein hemoglobin.

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Genetic Disorders

• The recessive allele that causes sickle-cell
  helps protect the cells of heterozygous
  individuals from the effects of malaria. Malaria
  is a disease caused by a parasitic protozoan that
  invades red blood cells.

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Genetic Disorders

• Cystic Fibrosis (CF) a fatal recessive trait
  it is the most common fatal hereditary disorder
  among Caucasians thick accumulation of mucus
• About 1 in 2,500 Caucasian infants in the U.S. is
  homozygous for the CF allele. There is no cure.

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Genetic Disorders

• Hemophilia- a condition that impairs the bloods
  ability to clot.
• It is a sex-linked trait. If the mutation
  appears on the X chromosome, which a male
  receives from his mother, he does not have a
  normal gene on the Y chromosome to compensate.
  Therefore, he will develop hemophilia.

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Genetic Disorders

• Huntingtons Disease (HD) caused by a dominant
  allele located on an autosome symptoms-
  forgetfulness, irritability, loss of muscle
  control, spasms, severe mental illness and death.
• Unfortunately, most people who have the HD allele
  do not know they have the disease until after
  they have children. The disease is passed
  unknowingly from one generation to the next.

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Treating Genetic Disorders

• Gene therapy- replacing defective genes with
  copies of healthy ones allows scientists to
  correct certain recessive disorders.
• What has been done successfully with the CF gene?

Working cf genes were attached to a cold virus
which easily infects lung cells. Then, those
cells produce more working cells.
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Genetic Disorder
No

• Has this been successful in humans?
• Why?

Most people have built up immunity to the cold
virus and the lungs reject the virus and its cf
passenger.
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EOC Prep Question

• The mutated allele that causes Huntingtons
  disease is
• A. Sex-linked and recessive
• B. Sex-linked and dominant
• C. Autosomal and recessive
• D. Autosomal and dominant